Method and apparatus for encoding/decoding images using a motion vector
The present invention relates to a method and apparatus for encoding/decoding image using a motion vector.According to one embodiment of the present invention, an image-decoding method is provided. The image-decoding method comprises the following steps: clipping a motion vector of a reference picture with a predetermined dynamic range so as to generate a clipped motion vector; storing the clipped motion vector in a buffer; deriving a motion vector of a block to be decoded using the motion vector stored in the buffer; and performing inter-prediction decoding using the motion vector of the block to be decoded. According to the present invention, the size of a memory space required to store a motion vector may be reduced.
1. An image decoding apparatus comprising:
a reference picture buffer to store a reference picture; and
one or more processors to
calculate a scaling factor based on a picture order count of the reference picture,
clip the scaling factor in a first predetermined range,
scale a motion vector of the reference picture based on the clipped scaling factor,
clip the scaled motion vector of the reference picture in a second predetermined range, and
generate a prediction block based on the reference picture and the clipped scaled motion vector of the reference picture,
wherein the motion vector of the reference picture is determined as a motion vector of a collocated block in the reference picture,
wherein the motion vector of the collocated block is determined by performing the ordered steps of:
calculating a first position corresponding to a right-bottom position representing a position displaced from an upper-left position of a current block in a current picture by the current block's height and width,
determining a first block covering the first position in the reference picture,
determining whether the first block is coded in an intra prediction mode,
calculating, when the first block is coded in an intra prediction mode, a second position corresponding to a central position of the current block in the current picture, and
determining a second block covering the second position in the reference picture.
2. The image decoding apparatus of claim 1 , wherein the second predetermined range is a fixed value range.
3. The image decoding apparatus of claim 1 , wherein the motion vector of the reference picture is stored in a predetermined block unit, and
wherein the motion compensator is further configured to generate the prediction block using the motion vector of the reference picture stored in the predetermined block unit.
4. The image decoding apparatus of claim 2 , wherein the motion compensator is further configured to clip X and Y components of the scaled motion vector in a same fixed value range.
5. The image decoding apparatus of claim 1 , wherein the motion vector of the reference picture is a motion vector of a block decoded in an inter-prediction mode.
6. An image encoding apparatus comprising:
a reference picture buffer to store a reference picture;
one or more processors to generate a motion vector of a current block and a prediction block of the current block based on the reference picture; and
an encoder configured to
calculate a scaling factor based on a picture order count of the reference picture,
clip the scaling factor in a first predetermined range,
scale a motion vector of the reference picture based on the clipped scaling factor,
clip the scaled motion vector of the reference picture in a second predetermined range, and
encode the motion vector of the current block based on the clipped scaled motion vector of the reference picture,
wherein the motion vector of the reference picture is determined as a motion vector of a collocated block in the reference picture,
wherein the motion vector of the collocated block is determined by performing the ordered steps of:
calculating a first position corresponding to a right-bottom position representing a position displaced from an upper-left position of a current block in a current picture by the current block's height and width,
determining a first block covering the first position in the reference picture,
determining whether the first block is coded in an intra prediction mode,
calculating, when the first block is coded in an intra prediction mode, a second position corresponding to a central position of the current block in the current picture, and
determining a second block covering the second position in the reference picture.
7. A non-transitory computer-readable storage medium storing a bitstream, wherein the bitstream is generated by an image encoding apparatus,
wherein the image encoding apparatus comprises
a reference picture buffer to store a reference picture;
a motion estimator to generate a motion vector of a current block and a prediction block of the current block based on the reference picture; and
one or more processors to
calculate a scaling factor based on a picture order count of the reference picture,
clip the scaling factor in a first predetermined range,
scale a motion vector of the reference picture based on the clipped scaling factor,
clip the scaled motion vector of the reference picture in a second predetermined range, and
encode the motion vector of the current block based on the clipped scaled motion vector of the reference picture,
wherein the motion vector of the reference picture is determined as a motion vector of a collocated block in the reference picture,
wherein the motion vector of the collocated block is determined by performing the ordered steps of:
calculating a first position corresponding to a right-bottom position representing a position displaced from an upper-left position of a current block in a current picture by the current block's height and width,
determining a first block covering the first position in the reference picture,
determining whether the first block is coded in an intra prediction mode,
calculating, when the first block is coded in an intra prediction mode, a second position corresponding to a central position of the current block in the current picture, and
determining a second block covering the second position in the reference picture.